Sergio Moya

Hollow Polymer Shells from Biological Templates: Fabrication and Potential Applications

Three-dimensional ultrathin polymer shells have been produced by a combination of step-by-step adsorption of polyelectrolytes on glutaraldehyde-treated human erythrocytes and subsequent solubilization of the cytoplasmatic constituents by means of a deproteinizing agent. The obtained hollow films preserve both the size and shape of the templating cells. This opens a pathway for the fabrication of polymeric capsules within a wide range of size and shape by using various biological templates. They may have exciting potential applications, such as templates for nanocomposites, as containers for a large class of materials, or as cages for chemical reactions. The thickness of the films can be adjusted over a large range: from a few nm up to several tens of nm. The polymer shells are permeable to small molecules and ions but not to macromolecules. An increase in the ionic strength of the solution up to 100 mmol make the capsules permeable for proteins. Permeability and conductivity studies have provided evidence that the adsorption of lipids on polyelectrolyte layers is a means of producing capsules with controlled permeability properties. 6-Carboxyfluorescein and Rhodamin 6G were precipitated within the capsules.

Layer by layer chitosan/alginate coatings on poly(lactide-co-glycolide) nanoparticles for antifouling protection and Folic acid binding to achieve selective cell targeting.

Polyelectrolyte multilayers (PEMs) composed of two natural polysaccharides-chitosan (Chi) and alginate (Alg) were deposited by Layer by layer (LbL) assembly on top of biocompatible poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs). Folic acid (FA) or FA grafted poly(ethylene glycol) (PEG-FA) were covalently bounded to the PEMs via carbodiimide chemistry. The assembly of biocompatible PEMs was monitored on planar surfaces by means of the quartz crystal microbalance with dissipation (QCM-D) technique and on top of PLGA NPs by means of ζ-potential measurements. BSA was used as model protein to characterize protein adsorption on PEMs. QCM-D showed protein deposition could not be observed on the Chi/Alg multilayer, for both Chitosan and Alginate as top layers. Finally, cellular uptake experiments were carried out by co-culture of HepG2 cells in presence of NPs. Flow Cytometry and confocal laser scanning microscopy (CLSM) were used to investigate the influence of the surface chemistry of the NPs on uptake. For the HepG2 cell line significantly less uptake of PLGA NPs coated with Chi/Alg than the bare NPs was observed but the uptake increased after attachment of FA molecules.

Microencapsulation by means of step-wise adsorption of polyelectrolytes.

Step-wise adsorption of polyelectrolytes is used for the fabrication of microand nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed.Step-wise adsorption of polyelectrolytes is used for the fabrication of micro- and nanocapsules with determined size, capsule wall composition and thickness. The capsule walls made of polyelectrolyte multilayers exclude high molecular weight compounds. Assembling of lipid layers onto these polyelectrolyte capsules prevents the permeation of small dyes. Encapsulation of magnetite nanoparticles is demonstrated and the features of these novel capsules are discussed.

Biodistribution of Different Sized Nanoparticles Assessed by Positron Emission Tomography: A General Strategy for Direct Activation of Metal Oxide Particles

The extraordinary small size of NPs makes them difficult to detect and quantify once distributed in a material or biological system. We present a simple and straightforward method for the direct proton beam activation of synthetic or commercially available aluminum oxide NPs (Al2O3 NPs) via the 16O(p,α)13N nuclear reaction in order to assess their biological fate using positron emission tomography (PET). The radiolabeling of the NPs does not alter their surface or structural properties as demonstrated by TEM, DLS, and ζ-potential measurements. The incorporation of radioactive 13N atoms in the Al2O3 NPs allowed the study of the biodistribution of the metal oxide NPs in rats after intravenous administration via PET. Despite the short half-life of 13N (9.97 min), the accumulation of NPs in different organs could be measured during the first 68 min after administration. The percentage amount of radioactivity per organ was calculated to evaluate the relative amount of NPs per organ. This simple and robust activation strategy can be applied to any synthetic or commercially available metal oxide particle.

Polyelectrolyte multilayer capsules templated on biological cells: core oxidation influences layer chemistry.

Abstract Polyelectrolyte multilayer capsules have been fabricated in aqueous media by step-wise assembling of sodium polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH) on human red blood cells and melamine formaldehyde resin particles as templates, followed by removal of these templates by two different procedures. The melamine formaldehyde core can be dissolved in pH 1.1. The removal of the cell cores was achieved by an oxidation with sodium hypochlorite solution (pH 12). The effect of these treatments on the chemical composition of the capsules and of a randomly formed polyelectrolyte complex was studied. The melamin resin templated capsules have basically the same composition as the untreated complex revealing no chemical changes induced by the acid. But about 20% of the total hollow capsules mass can be attributed to a rest of melamin resin. The treatment with NaOCl solution changed the chemical composition of the capsules drastically. The amino groups of polyallylamine were oxidized to nitriles, nitroso-, nitro-, azo- and carbonyl groups. Positive charges disappeared. Covalent bonds were formed which crosslink the polymer chains. Simultaneously, the amount of PSS is strongly reduced to 10% of the original value. The stability of the capsules can be understood as a result of crosslinking and hydrophobic interactions. The cell templated capsules are monodisperse, being replicas in size and shape of the template but their chemical composition is different compared with the initial polyelectrolyte multilayer film. The altered chemical properties are responsible for new physical and mechanical properties such as higher elasticity, high chemical stability, as well as selective adsorption and permeation for charged ions.

Highly Efficient Transition Metal Nanoparticle Catalysts in Aqueous Solutions

A ligand design is proposed for transition metal nanoparticle (TMNP) catalysts in aqueous solution. Thus, a tris(triazolyl)-polyethylene glycol (tris-trz-PEG) amphiphilic ligand, 2, is used for the synthesis of very small TMNPs with Fe, Co, Ni, Cu, Ru, Pd, Ag, Pt, and Au. These TMNP-2 catalysts were evaluated and compared for the model 4-nitrophenol reduction, and proved to be extremely efficient. High catalytic efficiencies involving the use of only a few ppm metal of PdNPs, RuNPs, and CuNPs were also exemplified in Suzuki-Miyaura, transfer hydrogenation, and click reactions, respectively.

A Highly Active and Magnetically Recoverable Tris(triazolyl)–CuI Catalyst for Alkyne–Azide Cycloaddition Reactions

Nanoparticle-supported tris(triazolyl)-CuBr, with a diameter of approximately 25 nm measured by TEM spectroscopy, has been easily prepared, and its catalytic activity was evaluated in the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. In initial experiments, 0.5 mol % loading successfully promoted the CuAAC reaction between benzyl azide and phenylacetylene, in water at room temperature (25 °C). During this process, the iron oxide nanoparticle-supported tris(triazolyl)-CuBr displayed good monodispersity, excellent recoverability, and outstanding reusability. Indeed, it was simply collected and separated from the reaction medium by using an external magnet, then used for another five catalytic cycles without significant loss of catalytic activity. Inductively coupled plasma (ICP) analysis for the first cycle revealed that the amount of copper leached from the catalyst into the reaction medium is negligible (1.5 ppm). The substrate scope has been examined, and it was found that the procedure can be successfully extended to various organic azides and alkynes and can also be applied to the one-pot synthesis of triazoles, through a cascade reaction involving benzyl bromides, alkynes, and sodium azide. In addition, the catalyst was shown to be an efficient CuAAC catalyst for the synthesis of allyl- and TEG-ended (TEG=triethylene glycol) 27-branch dendrimers.

Lipid layers on polyelectrolyte multilayer supports

The mechanism of formation of supported lipid layers from phosphatidylcholine and phosphatidylserine vesicles in solution on polyelectrolyte multilayers was studied by a variety of experimental techniques. The interaction of zwitterionic and acidic lipid vesicles, as well as their mixtures, with polyelectrolyte supports was followed in real time by micro-gravimetry. The fabricated lipid–polyelectrolyte composite structures on top of multilayer coated colloidal particles were characterized by flow cytometry and imaging techniques. Lipid diffusion over the macroscopic scale was quantified by fluorescence recovery after photobleaching, and the diffusion was related to layer connectivity. The phospholipid–polyelectrolyte binding mechanism was investigated by infrared spectroscopy. A strong interaction of polyelectrolyte primary amino groups with phosphate and carboxyl groups of the phospholipids, leading to dehydration, was observed. Long-range electrostatic attraction was proven to be essential for vesicle spreading and rupture. Fusion of lipid patches into a homogeneous bilayer required lateral mobility of the lipids on the polyelectrolyte support. The binding of amino groups to the phosphate group of the zwitterionic lipids was too weak to induce vesicle spreading, but sufficient for strong adsorption. Only the mixture of phosphatidylcholine and phosphatidylserine resulted in the spontaneous formation of bilayers on polyelectrolyte multilayers. The adsorption of phospholipids onto multilayers displaying quarternary ammonium polymers produced a novel 3D lipid polyelectrolyte structure on colloidal particles.

Surface engineered Poly(lactide-co-glycolide) nanoparticles for intracellular delivery: uptake and cytotoxicity--a confocal raman microscopic study.

Confocal Raman Microscopy (CRM) is used to study the cell internalization of poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) fabricated by emulsion techniques with either poly(ethylene imine) (PEI) or bovine serum albumin (BSA) as surface stabilizers. HepG2 cells were exposed to PEI and BSA stabilized PLGA NPs. Spontaneous Confocal Raman Spectra taken in one and the same spot of exposed cells showed bands arising from the cellular environment as well as bands characteristic for PLGA, proving that the PLGA NPs have been internalized. It was found that PLGA NPs preferentially colocalize with lipid bodies. The results from Raman spectroscopy are compared with flow cytometry and confocal scanning laser microscopy (CLSM) data. The advantages of CRM as a label-free technique over flow cytometry and CLSM are discussed. Additionally, cell viability studies by means of quick cell counting solution and MTT tests in several cell lines show a generally low toxicity for both PEI and BSA stabilized PLGA NPs, with BSA stabilized PLGA NPs having an even lower toxicity than PEI stabilized.

Polyelectrolyte coated PLGA nanoparticles: templation and release behavior.

Poly[(D,L-lactide)-co-glycolide] nanoparticles coated with polyethyleneimine on their surface were prepared by an emulsification-solvent evaporation method and subsequently surface modified by LBL assembly. The assembly of poly(acrylic acid) and polyethyleneimine on a planar substrate and on the PLGA nanoparticles was monitored by QCM-D, zeta-potential, flow cytometry and TEM. Carboxylic and amino groups in the multilayers were crosslinked by carbodiimide condensation, which was also later used to graft poly(ethylene glycol) (PEG). Rhodamine 6G, 5(6)-carboxyfluorescein and fluorescein were incorporated into the nanoparticles and their release profiles were recorded at 60 degrees C and at 37 degrees C for rhodamine 6G, for nanoparticles with a multilayer coating, and those that were crosslinked and grafted with PEG.